Orthodontic brackets are used in orthodontic treatments for moving one or more teeth from an initial position (sometimes referred to as malposition or malocclusion) to a desired position in a patient's dentition. For example by an orthodontic treatment the patient's teeth may be moved such that their labial sides are aligned with each other to achieve or maximize an aesthetically pleasant appearance of the overall dentition. Further in some cases one or more teeth may be moved to correct a malocclusion. The movement of teeth is typically achieved by a pre-biased elastic archwire which is attached via brackets to the teeth, and which applies a force to the teeth toward the desired position over a longer time period.
The brackets are typically bonded to the patient's teeth and the elastic archwire is connected to the brackets. The archwire is typically shaped to match with the position of the brackets in the desired position of the teeth so that in the initial position of the teeth the archwire can be connected to the brackets only under pretension. Accordingly the archwire once it is installed to the brackets is elastically deformed or pre-biased in the initial position of the teeth and the reset force toward the non-deformed shape of the archwire causes the teeth to be urged toward the desired position.
So-called treatment planning systems have been used to determine the desired position of the teeth in a computer simulation in advance of any actual treatment. Such a planning system helps for example for avoiding collisions between the teeth and brackets in tooth positions outside the initial position, and further allows for the brackets and the archwire to be designed and arranged to match with a variety of clinical situations, for example with the position of the teeth in the initial position, in the desired position, and positions between. In particular for lingual brackets such treatment planning is widely used. Lingual brackets often have a customized design individually for every tooth and patient because, other than the labial surfaces of a tooth, the lingual surfaces greatly vary in shape relative to each other so that a “one fits all” bracket shape typically cannot be used. Some treatment planning systems also allow for designing such customized brackets which precisely match a tooth surface and the required clinical situations of a patient. Accordingly customized brackets typically have to be precisely placed at positions on the teeth which are predetermined during the treatment planning. For facilitating a precise placement of the brackets on a patient's teeth and for the orthodontist's reference, the brackets are often provided prepositioned on a plaster model replicating the patient's teeth.
Such a plaster model on which the brackets are placed is sometimes used in orthodontics to make a so-called transfer tray for facilitating the placement of the bracket on a patient's teeth. A transfer tray typically is adapted to hold a complete set of brackets at the predetermined position and allow the brackets to be placed and bonded on the teeth in one step.
For example U.S. Pat. No. 7,020,963 discloses an indirect bonding apparatus is made by initially placing spacer material over a replica of the patient's tooth structure. A tray is then formed over the spacer material and hardened. Next, the spacer material is removed from the tooth replica and orthodontic appliances are placed on the replica at desired locations. A matrix material is placed between the tray and the replica and allowed to harden. The tray and the brackets (which are embedded in an interior wall of the tray) are then detached from the plaster model.
In another example as disclosed in WO 01/80761 a treatment planning software virtually superimposes brackets on teeth to generate a three-dimensional model comprising the three-dimensional tooth objects plus the virtual brackets at their intended locations. This three-dimensional model is supplied to a stereo lithography (SLA) instrument for manufacturing a plastic model of the teeth with the brackets superimposed thereon. A thermoplastic foil is placed above the SLA model and the model and foil are placed within a pressure chamber. The chamber is pressurized so that the foil envelops the dentition and the brackets. The foil thus obtains small indentations where the brackets can be located.
Although a variety of different solutions for precise positioning of brackets are available there is still a desire to provide a solution which helps maximizing the precision of the positioning and minimizing costs in the orthodontic treatment.